In all of entertainment, no figure is more beloved than Opah! Her networks make the most money. Her endorsements confer instant fame and wealth. Her personal life is the subject of profound fascination and scrutiny. She is what all Americans aspire to be…a veritable queen who transcends…

Opah!

Wait…Opah? That’s a big orange fish! Also known as moonfish, opahs consist of two species (Lampris guttatus and Lampris immaculates) which are alone in their own small family the Lampridae. Their closest relatives are the magnificent ribbonfishes like the crestfishes and oarfish! They are discoid fish with orange bodies (speckled with white) and with bright vermillion fins. Opahs do not give away cars or support quack psychiatrists and physicians, but, they are much in the news right now anyway. To the immense surprise of ichthyologists and zoologists, a research team from the NOOA has discovered that Opahs are warm-blooded—in a way. They are the only endothermic fish known to science.

Lampris guttatus (NOAA)

Being warm-blooded allows animals in the deep ocean to think and move more swiftly than the more ascetic and staid dwellers of the deep (most creatures of the ocean bottom are usually slow and placid in order to conserve energy–like the tripod fish). Ocean birds and marine mammals have long used this to their advantage. They gulp air from the surface and then dive deep to catch slower moving fish, squid, and invertebrates from the cold depths.

A stamp from French Southern and Antarctic Territories showing Lampris immaculatus

Other high-speed predatory fish (certain species of sharks and sportsfish) can warm key muscle groups using heat exchanging blood vessels in order to gain a burst of super speed, but these fish rapidly lose their heat—and the related speed advantages–as their blood circulates through their gills. This is one of the reasons sharks and marlins lunge and then return to slow measured swimming.

The opah appears to produce the majority of its heat by constantly flapping its pectoral fins. The warmth thus generated is not lost through the opahs’ gills. Critically, these fish possess unique insulated networks of blood vessels between their hearts and gills. The residual heat is removed from blood headed through the gills and then restored as it goes back through the heart. Their weird circular shape and comparatively large size are additional adaptations to help them conserve this warmth.

An opah near San Clemente Island (Jane J. Lee for National Geographic)

Marine biologists know surprisingly little about opahs (especially considering that the fish have long been known to fishermen and diners). Opahs live in the mesopelagic depths 50 to 500 meters (175 to 1650 feet) beneath the surface but it now seems they might make deeper hunting forays into the true depths. They are solitary hunters which live on shrimp, krill, and small fish. Opahs are approximately the size of vehicle tires. The smaller species (Lampris immaculatus) is like a big car tire and reaches a maximum of 1.1 m (3.6 ft). The larger species, Lampris guttatus, can become as large as an industrial lorry tire and can attain a length of 2 m (6.6 ft). the largest opahs weight up to 270 kg (600 lb).

Spotted Opah larva (Lampris guttatus)

Larval opahs resemble the larvae of oarfish (they are long and ribbonlike with strange protuberances. The main predators of Opahs are the great sharks…and humankind. Because of predation from this latter species which is endlessly hungry the survival of the opahs has grown less certain. It is believed that they have a low population resilience, but this…like their numbers and their lifestyle is unknown to science. We only just found they were warm-blooded earlier this month!